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Correct answer is (a) Nichrome

For explanation: Most of the metals obey Ohm’s LAW and they are called ohmic conductors. WHEREAS semiconductors are non-ohmic. Nichrome METAL is an ohmic conductor in which the V-I CHARACTERISTIC has a STRAIGHT line passing through the origin.

Correct answer is (c) 0.018 ms^-1

Easiest explanation: Drift velocity = Mobility × ELECTRIC field.

It can be REARRANGED as,

Drift velocity = \(\frac {(mobility \, \TIMES \, Potential \, DIFFERENCE)}{LENGTH}\).

Drift velocity = \(\frac {(9 × 10^{-5} \times 100)}{0.5}\) = 0.018 ms^-1.

Right answer is (c) ohm METRE

Best EXPLANATION: Resistivity = \(\FRAC {(Resistance \, \TIMES \, Area)}{LENGTH}\)

SI unit of resistivity=\(\frac {(ohm \, \times \, metre^2)}{metre}\)

 = ohm metre.

The CORRECT option is (a) True

Explanation: The emf of a CELL depends upon the NATURE of ELECTRODES, nature and concentration of ELECTROLYTE used in the cell and its temperature as well. Emf of a cell is inversely proportional to the concentration of the electrolyte.

The correct choice is (b) Temperature of the electrolyte

The best explanation: Internal RESISTANCE is defined as the resistance OFFERED by the electrolyte and electrodes of a CELL when the current flows through it. Internal resistance DEPENDS on distance between the electrodes, the nature of electrodes and electrolyte, and area of the electrode immersed in the electrolyte. So, that leaves temperature of the electrolyte out, which is the answer.

Correct answer is (b) False

To explain I would SAY: Electric power can ALSO be calculated or represented in other ways, such as: Power = voltage × CURRENT; Power = current^2 × resistance; Power = \(\frac {voltage^2}{resistance}\). In this case, we can use the EQUATION – Power = \(\frac {voltage^2}{resistance}\). Voltage = 300 V; Resistance = 100 ohms

Power = \(\frac {300 \times 300}{100}\)

= 900 Watts

Therefore, the power consumed by a 300 V BULB, having a resistance of 100 ohms, is 900 Watts.

Right choice is (c) Conductors

To explain I would SAY: Conductors have low resistivities in the range of 10^-8 Ωm to 10^-6 Ωm. Metals are GOOD conductors. Conductors are objects or types of material that allows the flow of charge in ONE or more directions, and a result, the resistance offered against the flow of charge will be less.

The CORRECT answer is (b) [M^0 L^0 T^0 A^1]

EXPLANATION: The flow of charge per unit time is defined as current. The FUNDAMENTAL unit of current is Ampere (named after ANDRE Marie Ampere).

Hence the DIMENSIONAL formula of electric current is [M^0 L^0 T^0 A^1].

Right ANSWER is (C) Alloys have a large temperature coefficient

To explain: Alloys have a HIGH value of resistivity. They have a very small temperature coefficient. So their resistance does not CHANGE appreciably even for several DEGREES rise of temperature. That leaves the answer – alloys have a large temperature coefficient.

Right option is (b) False

For EXPLANATION: The resistivity of semiconductors and INSULATORS DECREASES exponentially with the increase in TEMPERATURE. This is because the number density of FREE electrons increases exponentially with the increase in temperature.

Correct option is (d) CURRENT ELECTRICITY

The explanation: The study of MOTION or dynamics of charges constitute an electric current. Therefore, the study of electric charges in motion is called current electricity.

Right choice is (b) Conductivity, ohm^-1 m^-1

The best EXPLANATION: Conductivity = \(\frac {1}{Resistivity}\)

SI unit of conductivity = \(\frac {1}{ohm \, meter}\)

= ohm^-1 m^-1.

Correct answer is (d) 0.5 unit

The best I can explain: The NUMBER of units of electricity consumed is

n = \(\frac {(TOTAL \, wattage \, \TIMES \, TIME \, in \, hour)}{1000}\)

Total wattage = 100 WTime in hour = 5 hours

Therefore,n = \(\frac {100 \times 5}{1000}\)

= 0.5 units

So, the number of units of electricity consumed is 0.5 units.

The correct answer is (c) ELECTRONIC current

Best explanation: The carriers of electric current are electrons. The current in a circuit is DUE to the flow of electrons. THEREFORE, the direction of the CONVENTIONAL current is OPPOSITE to the direction of flow of electrons.

The correct CHOICE is (b) 11 ohms

The EXPLANATION is: Emf (e) = 6V; Internal RESISTANCE (r) = 1 ohms; Current (I) = 0.5A

Required equation: I = \(\frac {e}{R}\) + r

0.5 = \(\frac {6}{R}\) + 1

R = \(\frac {(6 – 0.5)}{0.5}\)

R = 11 ohms

Therefore, the resistance of the resistor is 11 ohms.

Correct choice is (C) one JOULE per second

The BEST explanation: WATT is the SI unit of power. Power = \(\FRAC { work \, done}{time}\). The SI unit of work done is the same as energy, that is, joule and that of time is seconds. Therefore, one watt is equal to one joule per second.

Right answer is (a) Resistivity increases and conductivity decreases

The best I can explain: The resistivity of a metal increases and the conductivity decreases with the INCREASE in TEMPERATURE. With an increase in temperature, the free electrons COLLIDE more frequently with the metal IONS. The mean collision time also decreases.

The correct choice is (a) Scalar quantity

For explanation: The electric CURRENT is a scalar quantity. Laws of ordinary algebra are used to ADD electric CURRENTS and the law of VECTOR algebra are not applicable.

Right CHOICE is (a) 1:3

For explanation: We can consider the relation that INCLUDES power and RESISTANCE, i.e.Power = \(\frac {voltage^2}{resistance}\). SINCE, the resistors are connected in parallel, the voltage across them will be the same. From this relation, power and resistance are inversely proportional to each other.

Thus, \(\frac {P1}{P2} = \frac {R2}{R1} = \frac {1}{3}\)

So, the power dissipated is in the RATIO is 1:3.

The correct ANSWER is (c) TERMINAL potential DIFFERENCE is LESSER than emf of the cell

For EXPLANATION I would say: During discharging of a cell terminal potential difference, the terminal potential difference is lesser than the emf of the cell. The direction of current inside the cell is from negative terminal to positive terminal.

Correct answer is (a) True

The explanation: Yes, in parallel GROUPING of cells, we obtain more current. In parallel combination, the voltage remains the same and the RESISTANCE OFFERED is minimum. As more cells are added parallel to each other, then the resistance will keep reducing. As a RESULT, more current can be obtained.

Correct choice is (c) Nichrome

To explain I would say: ALLOYS have high RESISTIVITY. The resistivity of nichrome has WEAK temperature dependence. At absolute zero, a PURE metal has negligibly small resistivity while an alloy like nichrome has some RESIDUAL resistivity.

Correct answer is (a) Bakelite

To EXPLAIN I would say: INSULATORS are materials which do not conduct electric current, and thereby, offer high resistance to the FLOW of charges. Insulators LIKE bakelite and hard rubber have very high resistivities in the RANGE of 10^14 to 10^16 Ωm.

Right option is (b) False

The best I can explain: OHM’s LAW is not a fundamental law of nature. Some reasons for the failure of ohm’s law are: Potential DIFFERENCE MAY vary non-linearly with the current ; The V-I relationship may be non-unique; The VARIATION of current with potential difference may depend upon the sign of the potential difference applied.

Right choice is (a) True

The explanation: Yes, the equivalent overall resistance is SMALLER than the smallest resistor connected in parallel. This is because, the overall equivalent resistance of parallel COMBINATION is: Rp = \(\frac {1}{R_1} + \frac {1}{R_2} + \frac {1}{R_3}\). When the inverse of a resistance value is taken, the value obtained is lesser than the original value. THUS, the sum of inverse values will only provide a lesser value than the initial RESISTANCES.

Correct option is (c) Rs.138

To explain: NEW bulbs = 5; OLD bulbs = 7; Total WATTAGE of new bulbs = 5 × 50;

Total wattage of old bulbs = 7 × 50; TIME the new bulbs are kept on = 5 hours;

Time the old bulbs are kept on = 3 hours

The number of units of electricity consumed by new bulbs (n1) = \(\frac {(total \, wattage \, \times \, time \, in \, hours)}{1000}\)

= \(\frac {50 \times 5 \times 5}{1000}\) = 1.25

The number of units of electricity consumed by old bulbs (n2) = \(\frac {50 \times 7 \times 3}{1000}\) = 1.05Total BILL of electricity = number of units of electricity consumed × amount for one unit of electricity

= (n1 + n2) × 60

= (1.25 + 1.05) × 60

= 138

Therefore, his electricity bill will be Rs. 138.

Right choice is (a) It converts chemical energy to electrical energy

Best explanation: An electrochemical cell is a device which converts chemical energy to ELECTRIC energy, and maintains the flow of charge in a circuit. There are 2 types of electrochemical cells – GALVANIC cell and ELECTROLYTIC cell.

The CORRECT answer is (a) 3.6 × 10^6 J

The explanation: The COMMERCIAL unit of electric energy is kilowatt-hour (kWh).

1 kWh = 1000 Wh = 3.6 × 10^6J = one unit of electricity CONSUMED. The electric energy used in factories, industries and houses are measured in kWh.

Correct choice is (b) Wire-bound resistor

The best EXPLANATION: A wire bound resistor is an electrical passive component that limits current. Wire-bound RESISTORS are MADE by winding the wires of an ALLOY like manganin on an insulating base. They are relatively insensitive to temperature.

The correct choice is (C) SILICON

To explain I would say: Silicon is an example of a non-ohmic conductor. It EXHIBITS non-linear behaviour. After a certain voltage, the current decreases as the voltage INCREASES. The V-I PLOT for silicon is non-linear.

Right CHOICE is (B) False

Explanation: Free CHARGED particles exist in the upper strata of environment called the ionosphere. It is a region which is IONIZED by solar radiation and includes PARTS of thermosphere, mesosphere and exosphere.

Correct choice is (a) RS = R1 + R2 + R3

For explanation I would say: When three resistors are CONNECTED in series, then the equivalent RESISTANCE of this combination is Rs = R1 + R2 + R3. So, if 3 resistors having resistances 10, 15, and 20 ohms, are connected in series, then equivalent resistance of this combination is Rs = 10+15+20 = 45 ohms.

The correct choice is (b) Electric power = \(\frac {electric \, WORK \, done}{time \, TAKEN}\)

To explain I would say: Electric power is defined as the rate at which work is done by the SOURCE of EMF in maintaining the CURRENT in the electric circuit. So, the formula of electric power is:

Electric power (P) = \(\frac {electric \, work \, done}{time \, taken}\)

The correct option is (b) False

For explanation: The fourth band INDICATES the tolerance or POSSIBLE VARIATION in the percent of the INDICATED value. If the fourth band is absent, it implies the tolerance of the resistor is ±20%.

Right choice is (b) m^2V^-1s^-1

The explanation is: The SI UNIT of MOBILITY is m^2V^-1s^-1.

Mobility = \(\FRAC {Drift \, velocity}{Electric \, field}\)

SI unit = \(\frac {ms^{-1}}{Vm^{-1}}\) = m^2V^-1s^-1.

The correct CHOICE is (B) Series grouping

For explanation: When n identical cells, each of emf ‘E’ and internal resistance ‘r’ are connected to the external resistance ‘R’ in series, its called series grouping. In series grouping eeq = ne and REQ = nr Therefore, current in the circuit (I) = \(\frac {ne}{(R + nr)}\).

Correct CHOICE is (C) Constantan

For explanation: Alloys like constantan or manganin are used for making standard RESISTANCE coils due to their high resistivity values and very small TEMPERATURE coefficient.

The CORRECT option is (d) p-n junction diode

Easiest explanation: p-n junction diode consists of p-type and n-type semiconductors. The V-I relationship is non-linear. When a VOLTAGE is APPLIED across junction, very little current flows for the fairly high NEGATIVE voltage and a current begins to flow for much smaller positive (forward) bias. The magnitude of variation DEPENDS upon the sign of potential difference applied across it.

Right answer is (a) METALLIC conductor

The explanation is: ‘X’ is a metallic conductor. For small currents, it obeys OHMS’s law and its V-I GRAPH is a straight line. But when large currents are passed through the same conductor, it gets heated up and its resistance increases. It no longer obeys OHM’s law at higher currents.

Correct option is (b) The straight-LINE V-I graph PASS through the origin

To explain: The conductors which obey Ohm’s LAW are called Ohmic conductors. The linear relationship between voltage and current for these conductors hold good. The resistance (R=\(\FRAC {V}{I}\)) is independent of the current through the conductor. The magnitude of current changes linearly with voltage. Hence the V-I graph for ohmic conductors is a straight line PASSING through the origin.

Right OPTION is (a) 130.20 ms^-1

Explanation: DRIFT velocity = \(\frac {Current}{(number \, DENSITY \, of \, electrons \, \times \, charge \, on \, electron \, \times \, Area)}\).

=\(\frac {200}{(96 \times 10^{20} \times 1.6 \times 10^{-19} \times 10^{-3})}\)

= 130.20 ms^-1.